1. Field of Invention
The present invention relates to a new and improved S-duct for supplying air to a turbojet aircraft engine located within the fuselage of the aircraft. The S-duct of the present invention allows a high volume of high energy subsonic air to traverse the S-duct at a high pressure recovery ratio.
2. Background Description
S-duct technology is old in the art. Boeing Commercial Airplane Company was one of the original and principal developers of S-Duct technology in the early 1970's to supply air to a turbo jet engine mounted in the rear end of the fuselage for the well known 727 aircraft. During this early period Boeing developed an S-duct for the Pratt & Whitney JT8D engine.
This particular S-duct was somewhat successful. Boeing found that not all JT8D engines would work with all S-ducts. Engines would have to be selected for a high surge factor for placement as the aft engine, supplied by a conventional S-duct. Boeing's S-duct was also limited in the volume of high energy air that would actually traverse the longitudinal length of the S-duct and appear at the engine fan.
The high energy air f low problem was addressed by Boeing in later versions of the S-duct. Boeing's S-duct technology dictated that more air flow from a larger diameter S-duct would solve the high energy air flow problem. However, to Boeing's dismay the larger inlet to the S-duct did not result in more high energy air reaching the engine fan. The principal reason for this failure is that the larger the inlet, the slower the air moves in the duct, therefore less high energy air reaches the engine fan.
Present S-duct technology has many limitations, most of which are limitations imposed by the aircraft structure in the vicinity, of an S-duct for an aft engine. An example of such limitation is the Boeing 727 aircraft. The S-duct of that aircraft must traverse the rear pressure bulkhead and pass unobstructingly through a fixed dimensioned aperture in the front spar forging of the vertical tail fin on its way to the aft engine. Other limitations are Federal Aeronautics Administration (FAA) and the International Civil Aviation Organization (ICAO) increasing requirements for engine noise abatement in and around airports. These restrictions have performance penalities associated with them. These penalities may be overcome by using a much quieter and efficient engine, such as the Rolls Royce Tay 650 or 670 model engine.
The Tay series engine by Rolls Royce requires 30% more air flow than the JT8D engine by Pratt Whitney. That increase in air flow, according to present S-duct technology, would dictate a 30% larger S-duct. However, not many current aircraft have a fuselage that will support a 30% increase in S-duct size.
Therefore, due to aircraft structural limitations, governmental restrictions, and limited S-duct technology, a more efficient and quiet aircraft engine utilizing a S-duct is a longfelt but unresolved need in the aircraft industry.
Other objects, advantages and features of the present; invention will become apparent to those skilled in the art from the following discussion.